1. Field of the Invention
The present invention relates to a process and a device for managing intercellular transfers of communications in a GSM-type cellular radio communication system.
2. Discussion of the Background
It applies in particular to the implementing of cellular radio communication systems in an urban environment in which the density of traffic requires a multitude of cells and consequently a reduction in their size.
In these systems, such as those described, for example in Patent Applications DE-A-4 414 428 and EP-A-0 589 278, the radio coverage of a territory is achieved by using macrocells also termed umbrella cells, each of which encompasses a set of adjoining microcells, each cell possessing a transmit and receive base station. The base station of an umbrella cell is generally arranged at a spot which is high up with respect to the surface of the ground, on the roof of a building for example, and its transmission power is defined so as to enable it to broadcast information in a circular zone whose radius may reach several kilometers. In a different way each transmit/receive base station of a microcell services a zone of small radius which may reach a few hundred meters, and their transmit/receive aerials are generally sited below the level of the roof of buildings, on public lampposts for example.
The umbrella cell makes it possible to absorb the excess traffic appearing in a micro-cell and to manage the gaps in coverage in the micro-cellular deployment. The microcells allow an increase in traffic in a given zone, and make it possible to compensate for coverage hindered by obstacles. However, the construction of microcells of small dimensions gives rise to a complexity in the processing of the transfers of communications between microcells since the more the size of the microcells is reduced, the more it becomes necessary to manage the transfers between cells ever more frequently, and this is all the more so the larger the speed of movement of the mobiles in communication within the cellular network thus formed. This difficulty incurs risks of congestion of the multicellular network which takes a considerable time to manage the signalling signals which accompany each transfer. This difficulty is encountered in particular in GSM mobile radio networks in which no distinction is made between the mobiles in communication, apart from their power class, thus making it difficult to track mobiles in communication so as to offload the communications of the fast mobiles onto the umbrella cell.